Fiberoptic clearance detection system and method

A system comprising:

• a steam turbine comprising a rotor and a stator;
• a moisture resistant optical fiber probe comprising a plurality of optical fibers, at least one of the optical fibers comprising a transmission fiber and at least three of the optical fibers comprising signal fibers;
• a light source for providing light through the transmission fiber towards the steam turbine rotor;
• filters for receiving light from the signal fibers and for filtering out unwanted light;
• at least one photodetector for receiving filtered light from the filters;
• and
• a processor for using intensities of the signals from the at least one photodetector representative of light intensities at different wavelengths to detect a variation in distance between the steam turbine rotor and the steam turbine stator.